Here is a link to soem pictures of Poisson's spot I made using this method.
I used a #79 tap drill which gives about a 400um hole. I used a 35mW green
diode laser. I have included a diagram of the setup I used. Also tried this
with a 100W halogen lamp, but could not see anythong. My guess is the sun
would make a nice white light source. Wish I had a heliostat.

Tom Bauer

Wellesley College

http://www.wellesley.edu/Physics/Tbauer/Poisson/

tap-l@lists.ncsu.edu writes:

Tappers,

I used a high quality, ~$1,000 Melles-Griot green laser this time to do
Poisson's spot early this AM using my pinhole method. Here are the results:

The technique I employ does not require a beam expander. It requires only a
.010 mm pinhole.

Bill A's idea to use the Tap and Drill Size Gauge from McMaster Carr is
absolutely brilliant!

And an insight like that can only be discovered by reading tap-l.

Note that a .010 spatial filter is really, really big. Most optical spatial
filters are much, much smaller.

BTW I really want to sell people to look at Arnold Sommerfeld's Optics,
volume IV in his lectures on Theoretical Physics.

His discussion on Poisson's spot is amazing.

He discusses how you can use a circular metal disk as a lens to do
photography! This is great stuff, in the vein of pinhole photography
hobbyists. He says that in a laboratory in Moscow a dinner plate was held
up by someones hand and was used to image a Poisson's Spot 40 meters away!!
And this had to be done no later than 1949 when Sommerfeld published his
lecture series.

Sommerfeld's lecture series sits in a prominent place my Library, right next
to Feynman's Lectures Series, Sutton's Demonstration Experiments in Physics,
John Strong's Procedures in Experimental Physics and his Procedures in
Applied Optics. - JZ

I did not use a beam expander. I used an ultra cheap, low quality 15 year
old metrologic He Ne laser and a .010 mm pinhole. And a very long optical
rail, two meters in length is good.

Tomorrow I will do it again with a higher quality green laser.

You must first get a good pinhole diffraction image, which can be seen in
the first three photos. The longer distance between the viewing screen and
the pinhole the better because greater distance gives an improved image.
The distance I used was about 2 meters. Then place the circular disc in the
center of the pinhole diffraction spot. I used a small sphere about 5mm in
diameter mounted on a glass slide.

If you notice carefully the Poisson's spot is actually an image of the
pinhole diffraction!

Yes, the circular disc itself will act like a long focal length lens. The
Poisson spot is actually an image the light source!

I was just using a Pasco 72mm diverging lens that mounts to their magnetic
optics bench. That will spread a standard beam to a dot ~7cm at a distance
of 2m or so. I actually thought about the green laser I picked up at the
PIRA meeting for a brief second then filed that thought away until I looked
into the safety of it.

-Keith

NCSU

From: tap-l-owner@lists.ncsu.edu
[mailto: tap-l-owner@lists.ncsu.edu] On
Behalf Of David Maiullo

Sent: Monday, October 25, 2010 1:53 PM

To: tap-l@lists.ncsu.edu

Subject: Re: [tap-l] Poisson's spot

Tappers,

Nice discussion. I'm curious though, has anyone ever used or tried one of
the "new" super bright green (or other color) laser pointers to achieve this
effect? I never thought my neon/helium lasers were bright enough to get a
nice image and center spot, at least one that was easy to spot (no pun
intended). And no one has yet mentioned what beam spreader/expander they
use, just the type of laser or size of ball bearing/object...does anyone use
a small lens or microscope eyepiece? Describe the set up, please.

Dave/RU

On 10/25/2010 12:44 PM, Adam Beehler wrote:

Keith,

We have showed this effect for years with a 1.6mm sphere carefully glued to
a glass plate. The concentric rings are nice and the central spot is
bright; however, I had an instructor want to show the same thing with a
penny. Sure it works, but the image is less than desirable. One can see
the bright central "spot," but it is small, dim, and not without the yucky
radial arms as you mention. In both cases, I need to display the results
with a video camera to the whole class. I decided to mess around though
after his class to convince myself that what we were seeing with the penny
really was the effect and not due to some other optical phenomenom due to
the other lenses it went through before the class could see it. I'm
convinced it was real but learned it was easier to show with smaller
objects. I tried round objects of many different sizes. Some were 1/8" or
1/4" in diameter. They were a good balance between seeing a "central"
bright spot and way too many inner concentric rings to confuse things.
So...of course...the smaller the object the better the image, but the bigger
the object, the more conspicuous the bright central superposition. I hope
some of this helps.

Adam Beehler

I had an in

On 10/22/2010 6:28 PM, Keith Warren wrote:

So I tried to photograph this today and came up with this shot,

http://demoroom.physics.ncsu.edu/images/Poissons_spot.jpg

While the spot is definitely there, I was disappointed with the radial
lines. I thought I would see concentric lines. This shot is with a push
pin. I later shot with a BB glued to a microscope slide and saw the same
thing (minus the needle on the bottom). Also, this shot was with a red pen
laser dispersed through a pasco concave 72mm lens. For the BB shot I used a
Helium Neon laser and the same lens and similar results.

To borrow a timely relevant phrase from history... =
What
Cheer, Netop!

(http://www.wightmanfam=
ily.com/11misc.html )

Best, - =
JZ

On Fri, Nov 26, 2010 at 1:54 PM, Thomas J. Bauer = =
wrote:

Tappers,

Here is a link to soem pictures of Poisson's spot I made =
using
this method. I used a #79 tap drill which gives about a 400um hole. I =
used a
35mW green diode laser. I have included a diagram of the setup I used. =
Also
tried this with a 100W halogen lamp, but could not see anythong. My =
guess is
the sun would make a nice white light source. Wish I had a =
heliostat.

Tom Bauer

Wellesley College

http://www.wellesley.edu/Physics/Tbauer/Poisson/

tap-l@lists.ncsu.edu
writes:

Tappers,

I =
used a high
quality, ~$1,000 Melles-Griot green laser this time to do Poisson's spot =
early
this AM using my pinhole method. Here are the =
results:

The =
technique I
employ does not require a beam expander. It requires only a .010 =
mm
pinhole.

Bill =
A's idea
to use the Tap and Drill Size Gauge from McMaster Carr is absolutely =
brilliant!

And =
an insight
like that can only be discovered by reading =
tap-l.

Note =
that a
.010 spatial filter is really, really big. Most optical =
spatial
filters are much, much smaller.

BTW =
I really
want to sell people to look at Arnold Sommerfeld's Optics, volume IV in =
his
lectures on Theoretical Physics.

His =
discussion
on Poisson's spot is amazing.

He =
discusses
how you can use a circular metal disk as a lens to do photography! =
This
is great stuff, in the vein of pinhole photography hobbyists. He =
says
that in a laboratory in Moscow a dinner plate was held up by someones =
hand and
was used to image a Poisson's Spot 40 meters away!! And this had =
to be
done no later than 1949 when Sommerfeld published his lecture series. =

Sommerfeld's
lecture series sits in a prominent place my Library, right =
next to
Feynman's Lectures Series, Sutton's Demonstration Experiments =
in
Physics, John Strong's Procedures in Experimental Physics and his =
Procedures in
Applied Optics. - JZ

I =
did not use a
beam expander. I used an ultra cheap, low quality 15 year old =
metrologic
He Ne laser and a .010 mm pinhole. And a very long optical rail, =
two
meters in length is good.

Tomorrow I will
do it again with a higher quality green laser.

You =
must first
get a good pinhole diffraction image, which can be seen in the first =
three
photos. The longer distance between the viewing screen =
and the
pinhole the better because greater distance gives an improved image. =
The
distance I used was about 2 meters. Then place the circular disc =
in the
center of the pinhole diffraction spot. I used a small sphere =
about 5mm
in diameter mounted on a glass slide.

If =
you notice
carefully the Poisson's spot is actually an image of the pinhole =
diffraction!

Yes, =
the
circular disc itself will act like a long focal length lens. The =
Poisson
spot is actually an image the light source!

I =
was just
using a Pasco 72mm diverging lens that mounts to their magnetic =
optics
bench. That will spread a standard beam to a dot ~7cm at a =
distance of 2m
or so. I actually thought about the green laser I picked up =
at the
PIRA meeting for a brief second then filed that thought away until I =
looked
into the safety of it.

Nice
discussion. I'm curious though, has anyone ever used or tried one =
of the
"new" super bright green (or other color) laser pointers to =
achieve
this effect? I never thought my neon/helium lasers were bright =
enough to
get a nice image and center spot, at least one that was easy to spot (no =
pun
intended). And no one has yet mentioned what beam =
spreader/expander they
use, just the type of laser or size of ball bearing/object...does anyone =
use a
small lens or microscope eyepiece? Describe the set up, =
please.

Dave/RU

On =
10/25/2010
12:44 PM, Adam Beehler wrote:

Keith,

We =
have showed
this effect for years with a 1.6mm sphere carefully glued to a glass
plate. The concentric rings are nice and the central spot is =
bright;
however, I had an instructor want to show the same thing with a =
penny.
Sure it works, but the image is less than desirable. One can see =
the
bright central "spot," but it is small, dim, and not without =
the
yucky radial arms as you mention. In both cases, I need to display =
the
results with a video camera to the whole class. I decided to mess =
around
though after his class to convince myself that what we were seeing with =
the
penny really was the effect and not due to some other optical phenomenom =
due to
the other lenses it went through before the class could see it. =
I'm
convinced it was real but learned it was easier to show with smaller
objects. I tried round objects of many different sizes. Some =
were
1/8" or 1/4" in diameter. They were a good balance =
between
seeing a "central" bright spot and way too many inner =
concentric
rings to confuse things. So...of course...the smaller the object =
the
better the image, but the bigger the object, the more conspicuous the =
bright
central superposition. I hope some of this =
helps.

Adam =
Beehler

I =
had an in

On =
10/22/2010
6:28 PM, Keith Warren wrote:

So I =
tried to
photograph this today and came up with this shot,

http://demoroom.physics.ncsu.edu/images/Pois=
sons_spot.jpg

While the spot
is definitely there, I was disappointed with the radial lines. I =
thought
I would see concentric lines. This shot is with a push pin. =
I later
shot with a BB glued to a microscope slide and saw the same thing (minus =
the
needle on the bottom). Also, this shot was with a red pen laser =
dispersed
through a pasco concave 72mm lens. For the BB shot I used a Helium =
Neon
laser and the same lens and similar results.